The present invention relates to nonflammable silicone rubber compositions. Specifically, this invention relates to nonflammable silicone rubber compositions which exhibit a superior nonflammability and a reduced toxicity due to by-products generated during the vulcanization and forming process.
For making silicone rubbers nonflammable, platinum containing compounds have been proposed (Japanese patent application, Kokoku (examined) 44-2591, equivalent to CA 846,246-A). In addition to platinum, various compounds were proposed for further increased nonflammability: platinum containing compounds along with carbon black (Japanese patent application, Kokoku 47-16546, equivalent to U.S. Pat. No. 3,652,488); platinum containing compounds along with fumed titanium oxide (Japanese patent application, Kokoku 47-21826, equivalent to U.S. Pat. No. 3,035,874); platinum containing compounds along with azo compounds (Japanese patent application, Kokoku 51-24302, equivalent to U.S. Pat. No. 3,862,081); platinum containing compounds along with iron oxide (Japanese patent application, Kokoku 51-35501 and Kokoku 53-44501, equivalent to U.S. Pat. No. 4,110,300); platinum containing compounds along with triazole type compounds (Japanese patent application, Kokoku 53-16019, equivalent to U.S. Pat. No. 4,087,399 and Kokoku 62-61613, equivalent to U.S. Pat. No. 4,310,444); and platinum containing compounds along with organic silicone compounds having nitrogen containing organic groups and unsaturated groups (Japanese patent application, Kokoku 3-39550).
A high level of nonflammability, such as the V-0 or V-1 levels defined in UL-94 (Underwriters Laboratories), is achieved by the combined use of platinum containing compounds along with azo compounds, triazole compounds, and nitrogen containing organic silicone compounds. However, the usage of the azo compounds in combination has led to a wide variety in the levels of the resultant nonflammability, depending upon the structure of the azo compound. Among the azo compounds available on the market, 2, 2'-azobis(isobutyronitrile) has been the only azo compound which satisfies the required level of the nonflammability.
Even in the said Japanese patent application, Kokoku 51-24302, which reveals the usage of the azo compounds in combination, 2, 2'-azobis(isobutyronitrile) was the only example listed from the azo compounds of this type and other examples presented are the azo compounds having phenyl groups and the azo compounds having oxygens. No other dialkyl azo compounds, except 2,2'-azobis(isobutyronitrile), were specifically disclosed.
Further in the case of 2,2'-azobis(isobutyronitrile), tetramethyl succinodinitrile is produced by decomposition during the vulcanization and forming process which material possesses strong toxicity. However, the said Japanese patent application Kokoku 51-24302 did not address this problem, as well.
In addition, the combined use of triazole type compounds has a bag effect on workers due to the strong odor during the vulcanization and forming process. Further these compounds interfere with vulcanization, which troublesomely impairs the hardness and modulus of the cured products.
When organic silicone compounds having nitrogens are used in combination, the resultant nonflammability tends to be inferior for some types of the silicone rubber compositions. Therefore the silicone rubber compositions useful with such compounds are limited.
Therefore it is an object the present invention to offer nonflammable silicone rubber compositions which have a superior nonflammability while reducing the toxicity of the by-products generated by the vulcanization and forming process.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.